Wildflowers of Toronto's High Park
Ragweeds
Family: Composite/Aster
Genus: Ambrosia
Native to Ontario
Annual
Ragweed, common
A. artemisiifolia
Blooms: August to October
Habitat: Waste places
Height: up to 1 m
Leaves: fern-like
Female flower heads: single, inconspicuous, in axils of upper leaves.
Male flower heads: Long terminal spike bearing up to 50 florets which produce vast quantities of pollen. This is spread by wind and is a major cause of hay fever.
Ragweed, giant
A. trifida
Blooms: August to October
Habitat: Rich moist soil
Height: up to 4.5 m
Leaves: Opposite, with 3-5 palmate lobes
Male flower heads: terminal spikes. Female flower heads grow in leaf axils.
